DUNEDIN, Fla. -- The Major League Baseball Players Association has filed a grievance to MLB, claiming that four teams - the Tampa Bay Rays, Pittsburgh Pirates, Oakland Athletics and Miami Marlins - have not spent revenue-sharing money in the fashion intended by the collective bargaining agreement.

It's the first official salvo fired in a rancorous winter in which high-profile free agents have encountered a depressed market for their services, leaving dozens of veterans unemployed as spring training enters its third week.

MLBPA spokesman Chris Dahl confirmed to USA TODAY Sports that the grievance had been filed. It was first reported by the Tampa Bay Times.

While perhaps a dozen teams are taking a passive approach to competing this season - tanking to some, prudence to others - the Pirates, Rays, Marlins and Athletics have been perennial revenue-sharing recipients who remain in the bottom third of payrolls.

The union's complaint regards both the 2017 season and the current off-season.

"Hopefully, we’ll get to the bottom of it," Blue Jays pitcher J.A. Happ told USA TODAY Sports on Tuesday. "It’s been disappointing to see how the off-season has played out for a lot of guys. There’s a lot of really, really good players who can help a lot of teams that are unsigned still.

"You always wonder why that is."

The Pirates and Marlins, in particular, had a hand in depressing the market for free agents by flooding the pool with trade targets this year, including former All-Stars Giancarlo Stanton, Marcell Ozuna, Andrew McCutchen, Gerrit Cole and dynamic outfielder Christian Yelich.

The Pirates' payroll will be around $75 million this season. They and MLB lashed out at the union's grievance as without merit.

“The MLBPA’s grievance against the Pirates is patently baseless," said Pirates president Frank Coonelly in a written statement. "We look forward to demonstrating as much to the arbitrator if the MLBPA continues to pursue this meritless claim.

"As indicated when the MLBPA first expressed its 'concern' in a press release, the Pirates have always invested its revenue sharing receipts in a manner entirely consistent with the basic agreement."

"It is regrettable and that the MLBPA would react to a free agent market that is apparently not to its liking by filing a frivolous grievance against a club that has continued to invest heavily in all areas of its baseball operations notwithstanding steadily diminishing revenue sharing receipts.”

Blue Jays outfielder Curtis Granderson, a former player's representative to the union and executive council member, said the union does not take grievance filings lightly.

"It’s not going to be, let me throw some stuff out there because publicly, things haven’t gone the way people expected it to go," says Granderson, who signed a one-year, $5 million deal last month. "The union is very adept at getting as much research, as much knowledge as they can, before making a calculated move like this.

"It’s not a shot in the dark. There’s a reason behind what they’re doing."

The Athletics and Rays, the last major league teams sorely in need of a new stadium, rank 29th and 30th in revenue, but receive tens of millions of dollars in revenue sharing. The A's in the past two seasons have embarked on a more thorough rebuilding, and this season their projected payroll is around $60 million. The Rays, after an off-season of significant movement, should once again have a payroll above $70 million.

The A's revenue-sharing checks are being phased out by 2020 as other franchises appear intent on pressuring them to resolve their stadium situation.

Tampa Bay Rays owner Stuart Sternberg told the Times that the Rays are "beyond compliance" with revenue sharing spending requirements.

MLB responded in a statement e-mailed to USA TODAY Sports, saying: “We do not have concerns about the Pirates’ and Marlins’ compliance with the Basic Agreement provisions regarding the use of revenue sharing proceeds. The Pirates have steadily increased their payroll over the years while at the same time decreasing their revenue sharing. The Marlins’ ownership purchased a team that incurred substantial financial losses the prior two seasons, and even with revenue sharing and significant expense reduction, the team is projected to lose money in 2018. The Union has not informed us that it intends to file a grievance against either team.”

Tuesday, the union added the Athletics and Rays to the hit list, while a player population that seems ready for a fight watches closely.

“You feel for the fans, because the fan bases want to see competitive teams out there," says Rich Hill, the Los Angeles Dodger lefty and former A's starter. "They want to see the best players, and there’s a lot of great players who are still out there that haven’t been signed. So there’s tremendous improvement that can be made for many clubs that for whatever reason has not come around.’’